The present invention relates to the manufacture of electronic devices. More particularly, the invention provides a device for planarizing a film of material of an article such as a semiconductor wafer. In an exemplary embodiment, the present invention provides an improved substrate support for the manufacture of semiconductor integrated circuits. However, it will be recognized that the invention has a wider range of applicability; it can also be applied to flat panel displays, hard disks, raw wafers, MEMS wafers, and other objects that require a high degree of planarity.
The fabrication of integrated circuit devices often begins by producing semiconductor wafers cut from an ingot of single crystal silicon which is formed by pulling a seed from a silicon melt rotating in a crucible. The ingot is then sliced into individual wafers using a diamond cutting blade. Following the cutting operation, at least one surface (process surface) of the wafer is polished to a relatively flat, scratch-free surface. The polished surface area of the wafer is first subdivided into a plurality of die locations at which integrated circuits (IC) are subsequently formed. A series of wafer masking and processing steps are used to fabricate each IC. Thereafter, the individual dice are cut or scribed from the wafer and individually packaged and tested to complete the device manufacture process.
During IC manufacturing, the various masking and processing steps typically result in the formation of topographical irregularities on the wafer surface. For example, topographical surface irregularities are created after metallization, which includes a sequence of blanketing the wafer surface with a conductive metal layer and then etching away unwanted portions of the blanket metal layer to form a metallization interconnect pattern on each IC. This problem is exacerbated by the use of multilevel interconnects.
A common surface irregularity in a semiconductor wafer is known as a step. A step is the resulting height differential between the metal interconnect and the wafer surface where the metal has been removed. A typical VLSI chip on which a first metallization layer has been defined may contain several million steps, and the whole wafer may contain several hundred ICs.
Consequently, maintaining wafer surface planarity during fabrication is important. Photolithographic processes are typically pushed close to the limit of resolution in order to create maximum circuit density. Typical device geometries call for line widths on the order of 0.5 xcexcm. Since these geometries are photolithographically produced, it is important that the wafer surface be highly planar in order to accurately focus the illumination radiation at a single plane of focus to achieve precise imaging over the entire surface of the wafer. A wafer surface that is not sufficiently planar, will result in structures that are poorly defined, with the circuits either being nonfunctional or, at best, exhibiting less than optimum performance. To alleviate these problems, the wafer is xe2x80x9cplanarizedxe2x80x9d at various points in the process to minimize non-planar topography and its adverse effects. As additional levels are added to multilevel-interconnection schemes and circuit features are scaled to submicron dimensions, the required degree of planarization increases. As circuit dimensions are reduced, interconnect levels must be globally planarized to produce a reliable, high density device. Planarization can be implemented in either the conductor or the dielectric layers.
In order to achieve the degree of planarity required to produce high density integrated circuits, chemical-mechanical planarization processes (xe2x80x9cCMPxe2x80x9d) are being employed with increasing frequency. A conventional rotational CMP apparatus includes a wafer carrier for holding a semiconductor wafer. A soft, resilient pad is typically placed between the wafer carrier and the wafer, and the wafer is generally held against the resilient pad by a partial vacuum. The wafer carrier is designed to be continuously rotated by a drive motor. In addition, the wafer carrier typically is also designed for transverse movement. The rotational and transverse movement is intended to reduce variability in material removal rates over the surface of the wafer. The apparatus further includes a rotating platen on which is mounted a polishing pad. The platen is relatively large in comparison to the wafer, so that during the CMP process, the wafer may be moved across the surface of the polishing pad by the wafer carrier. A polishing slurry containing chemically-reactive solution, in which are suspended abrasive particles, is deposited through a supply tube onto the surface of the polishing pad.
CMP is advantageous because it can be performed in one step, in contrast to past planarization techniques which are complex, involving multiple steps. Moreover, CMP has been demonstrated to maintain high material removal rates of high surface features and low removal rates of low surface features, thus allowing for uniform planarization. CMP can also be used to remove different layers of material and various surface defects. CMP thus can improve the quality and reliability of the ICs formed on the wafer.
Chemical-mechanical planarization is a well developed planarization technique. The underlying chemistry and physics of the method is understood. However, it is commonly accepted that it still remains very difficult to obtain smooth results near the center of the wafer. The result is a planarized wafer whose center region may or may not be suitable for subsequent processing. Sometimes, therefore, it is not possible to fully utilize the entire surface of the wafer. This reduces yield and subsequently increases the per-chip manufacturing cost. Ultimately, the consumer suffers from higher prices.
It is therefore desirable to improve the useful surface of a semiconductor wafer to increase chip yield. What is needed is an improvement of the CMP technique to improve the degree of global planarity that can be achieved using CMP.
The present invention achieves these benefits in the context of known process technology and known techniques in the art. The present invention provides an improved planarization apparatus for chemical mechanical planarization. Specifically, the present invention provides an improved planarization apparatus that precisely aligns an object for planarization and eliminates deformation of the object during planarization.
In an exemplary embodiment, the invention provides an apparatus having an edge support movably coupled to an edge of an object for supporting and positioning the object during planarization; a back support operatively coupled to the edge support, the back support having at least one surface for supporting a back side of the object during planarization. The surface for supporting the back side provides a substantially friction free interface between the surface and the back side of the object to allow the object to move across the surface of the back support.
In another specific embodiment, the invention can have a polishing head operatively coupled to the back support, the polishing head comprising a polishing pad, the polishing pad having a treatment surface and a center axis, the polishing head being rotatably coupled to a drive motor to rotate the treatment surface about the center axis to polish the object.
In another specific embodiment, the invention can have a drive operatively coupled to the edge support to rotate the object in a fixed plane on the back support during planarization, the fixed plane being substantially parallel to a treatment surface of a polishing pad. Alternatively, the invention can have a drive operatively coupled to the edge support, the object having a center axis, wherein the edge support rotates the object about its center axis in a fixed plane during planarization, the fixed plane being substantially parallel to a treatment surface of a polishing pad.
In the specific embodiments, the edge support can move the object in a predetermined pattern relative to the polishing pad, the pattern being in a fixed plane at least when a polishing pad contacts the object during planarization, the fixed plane being substantially parallel to a treatment surface of a polishing pad. The predetermined pattern is substantially radial, linear, continuous, discontinuous, or any combination thereof.
In another specific embodiment the edge support can have a plurality of rollers, the object and each of the rollers having a center axis, each of the rollers being movably coupled to the edge of the object such that at least one of the rollers rotates about its center axis to drive the object to rotate about its center axis. At least one of the rollers rotates about its center axis in a to drive the object to rotate about its center axis in a counterclockwise direction. Alternatively, the edge support can rotate about its center axis of the object thereby causing the object to rotate about the center axis of the edge support.
In a specific embodiment, a surface of the back support comprises a diameter that is substantially the same size as the polishing pad diameter for providing adequate support to the object during planarization. The back support can be an air bearing, a liquid bearing, or the equivalent. In the present invention, the back support tracks a polishing pad to provide support to the object during planarization. This prevents deformation of the object during planarization. A further understanding of the nature and advantages of the present invention may be realized by reference to the latter portions of the specification and attached drawings.